1. Field of the Invention
The present invention generally relates to an antenna apparatus which is employed in a wireless communication medium processing apparatus communicated with a wireless communication medium such as an RFID (Radio Frequency Identification), namely, an IC card, an IC tag, and the like, or which is employed in the wireless communication medium itself. More specifically, the present invention is directed to such an antenna apparatus which can be made thin and in low cost and can improve a communication characteristic thereof in a microwave system, and an electromagnetic induction system, and also, is directed to an adjusting method thereof.
2. Description of the Related Art
Conventionally, in an RFID medium, namely, a non-contact type IC card, or an IC tag, in such a case that an antenna characteristic thereof is adjusted, as represented in FIG. 10, the following adjusting operation has been performed. That is, a capacitor pattern 102 and an adjusting-purpose resistance pattern 103 have been formed within an antenna unit 105, and then, a resonant frequency of an antenna apparatus 101 and a Q value thereof have been adjusted by trimming, or etching these patterns 102 and 103 (refer to, for example, patent publication 1).    Patent Publication 1: JP-A-2001-10264    Patent Publication 2: JP-A-2006-287659
However, in the above-described adjusting method, the magnetic field of the adjusting-purpose resistance pattern 103 are not coincident with the same direction as the magnetic field of the antenna unit 105, but are exerted in such a manner that these magnetic fields are partially canceled with each other. As a result, the adjusting range of the resonant frequency of the antenna apparatus 101 becomes narrow. Also, in such a case that the resonant frequency of the antenna apparatus 101 is adjusted by the capacitor pattern 102, the below-mentioned problem occurs. That is, under high temperature and high humidity environments, a dielectric constant of a base material 104 is changed, so that the resonant frequency of the antenna apparatus 101 is changed.
In order to secure communication stabilities as to wireless communication processing apparatuses that establish communications with various sorts of wireless communication media and in the wireless communication media themselves, resonant frequencies of antenna apparatuses are required to be made coincident with desirable frequencies (for example, 13.56 MHz).
However, in the conventional antenna apparatuses, since the adjusting ranges of the resonant frequencies in the antenna patterns have been made narrow, the resonant frequencies could not be adjusted when these antenna apparatuses were assembled. As a result, a large number of inferior antenna apparatuses have been manufactured.
Also, while loop-shaped antenna patterns have been formed in such a manner that magnetic fields thereof are produced along the same direction to that of the loop-shaped antenna patterns, resonant frequencies of the antennas have been adjusted by changing turn numbers of the loops (refer to, for instance, patent publication 2).
However, since the resonant frequencies have been adjusted by changing the turn numbers, the resonant frequencies could not be adjusted during assembling of the antenna apparatuses.
Further, tolerance ranges of center frequencies in antenna apparatuses, which are required from manufacturers of a portable telephone have been narrowed year by year, and therefore, adjusting of resonant frequencies of the antenna apparatuses could be very hardly carried out.